The invention relates to an implant for fixing a bone plate in an opening of a bone plate.
During the performance of cranial operations access is gained by plate-shaped bone sections being sawed out of the skull bone. After completion of the operation, these have to be fixed in the opening made in the vault of the skull in order that they can become incorporated again in the old position. Implants consisting of several individual parts are known for fixing these bone plates in the opening of the vault of the skull. The individual parts are placed from the upper side and the lower side on the vault of the skull and on the inserted bone plate and thereby fix the bone plate in the vault of the skull. Although these known implants are very user-friendly and have proven their worth in practice, it is necessary to use multipart implants and to insert these with the aid of relatively complicated applicators.
The object of the invention is to create a generic implant which is of simpler construction than known implants and is usable without any special applicators.
This object is accomplished with an implant of the kind described at the outset, in accordance with the invention, in that it is designed as a U-shaped clip, with a bridge and two contact arms protruding transversely from the bridge, the contact arms being capable of receiving a bone plate between them and thereby fixing the clip on the bone plate with the contact arms lying against the upper side and the lower side, respectively, of the bone plate, and with at least one projection on the outer side of the bridge facing away from the contact arms for fixing the clip on the other bone plate so that a displacement of the clip relative to the other bone plate in the longitudinal direction of the bridge is prevented in at least one direction.
Owing to the above-described construction, it is possible to push several such implants designed as U-shaped clips onto a bone plate in such a way that the clips are held on the bone plate and that the bridge of the clips lies in front of the edge of the bone plate. A bone plate provided, for example, with three such clips can then be inserted into an opening in the vault of the skull in such a way that the projections on the clips prevent the bone plate from entering too far into the opening in the skull. The projections on the outer side of the clip thus determine the position of the bone plate with respect to the surface of the opening in the skull, and this is adequate for fixing the bone plate for the incorporating and healing process. Aside from that, the bone plate placed in the opening of the skull is positioned in the skull opening such that a mark on the inserted plate and a mark on the opening in the skull are in alignment with each other so that the bone plate is also positioned in the circumferential direction in the way in which it was originally arranged in the skull opening. These marks can, for example, be formed by the two halves of a trepanation opening made in the vault of the skull as preparation for the cutting-out of the bone plate.
The clips are preferably fixed on the bone section closing the opening in the vault of the skull. In principle, it is, however, also possible to fix the clips on the vault of the skull and to then place the bone section closing the opening in the opening. The projections on the clips held on the vault of the skull would then also prevent the bone section from sinking in too deeply, and the bone section would thereby be fixed in the opening in the skull.
The new implant is explained herein in conjunction with the positioning of a bone plate in an opening in the skull. It will, however, be understood that this implant will always be usable where a bone plate is to be positioned in an opening of another bone plate.
If the implants have only one projection on the outer side of the bridge, the bone plates will normally only be fixable in one direction relative to each other with such implants. Thus, a bone plate can only be prevented from sinking too deeply into the opening of the other bone plate. A fixing on both sides, on the other hand, is only possible when, in accordance with a preferred embodiment, several projections are provided to center the other bone plate relative to the clip in the longitudinal direction of the bridge. The cooperation of several projections thus makes it possible to prevent displacement of the implant relative to the other bone plate in both directions and to thereby achieve a definite positioning of the two bone plates relative to each other.
Provision is made in a preferred embodiment for the bridge to have on its outer side at an end thereof a projection whose bearing surface on the other bone plate lies substantially in one plane with the bearing surface of the contact arm protruding from the bridge at this end thereof. The two bone plates to be fixed relative to each other can thereby be positioned in one plane. For example, the outer sides are aligned with each other in such a way that the bone plate inserted in an opening in the skull is in precise alignment with the outer side of the skull.
It is particularly advantageous for at least some of the projections on the outer side of the bridge and/or the bridge itself to be capable of elastic displacement or deformation such that the projections protrude less far from the edge of the bone plate on which the clip is held.
Insertion of the bone plate on which the clips are held thus results in a deformation of the bridges and/or the projections, so that after insertion the two bone plates are fixed relative to each other by the elastic force of these projections. These fixing forces can be pure clamping forces which are produced by the elastic deformation of the bridge and/or the projections. It can, however, also be a positive locking, namely when the projections undergo deformation when being inserted and after reaching the end position return to a less deformed initial position again in which the projections lie on both sides against the other bone plate. A combination of frictional engagement and positive locking is, of course, also possible.
Provision is made in a particularly preferred embodiment for the bridge to be of arcuate design in the longitudinal direction with a concave outer side and to be capable of elastic deformation into a more stretched position. Thus, the bridge of the clip positions itself in the central area thereof against the bone plate on which the clip is held, but in the end areas thereof against the other bone plate, which, after the positioning of the bone plates, results in a definite centering and fixing of the bone plates relative to each other.
It is expedient for the bridge to pass at least at one end thereof into the adjacent contact arm via a bend protruding outwardly relative to the bridge and forming a projection for fixing the clip on the other bone plate. Thus such a bend itself also forms a projection, so that it is not necessary to arrange additional parts on the outer side of the bridge. An elastic deformation of this projection is also possible by an arcuate design of the bridge itself, but also by an elastic compression of the bend.
Provision can be made for a projection to be formed on one side of the bridge by a projecting lug protruding transversely from the bridge. In this case, a lug is integrally formed on the outer side of the bridge, for example, by welding, so that it protrudes transversely from the bridge and forms a stop or a bearing surface for the other bone plate.
It is particularly advantageous for a projection to be formed on one side of the bridge by a bend, and for a further projection to be formed on the other side by such a projecting lug.
In particular, the projecting lug can have perforations for receiving bone screws so that after insertion of the bone plates, the projecting lug can be fixed on the other bone plate via bone screws, and an additional and permanent fixing of the two bone plates relative to each other is thereby achieved.
Furthermore, in accordance with a further preferred embodiment, such perforations for receiving bone screws can also be arranged in the contact arms, so that the clips can thereby be additionally fixed on the bone plate on which they are held by the contact arms.
It is also expedient for several projections to be arranged on the outer side of the bridge in the central area thereof and to be distributed over the length thereof. In particular, these projections can serve to establish a frictional engagement between the clip, on the one hand, and the other bone plate, on the other hand, and, in addition, the centering of the two bone plates relative to each other is thereby furthered.
In particular, these projections can be designed so as to be of sawtooth-shaped cross section so that the inserted bone plate is easily inserted, but not readily removable again.
It is also possible for the distance of the projections from the bone plate on which the contact arms fix the clip to be increasingly larger from one end of the bridge to the other. This also aids the centering of the bone plates relative to each other and facilitates the insertion with the formation of clamping forces which increase with the insertion depth.
The contact arms are preferably able to swivel apart in a resilient manner, so that the contact arms normally lie resiliently against the upper side and the lower side, respectively, of the bone plate, and thereby reliably fix the clip on the bone plate.
It is expedient for the contact arms to have at their free end projections which are directed towards each other so that certain differences in the thickness of the bone plates can thereby be compensated.
In particular, the projections can be formed by bends in the contact arms.
In accordance with a preferred embodiment, the fixing of the clips on the bone plate is promoted by the projections on the contact arms tapering to a point.
The contact arms can be of one-part construction. Provision is made in a preferred embodiment for each contact arm to be divided by cutouts extending from the free end thereof into at least two single arms arranged adjacent to each other. The clips are thereby also secured against tilting.
The contact arms can have a profile on their inner side facing the bone plate in order to strengthen the contact there between contact arms and bone plates. In particular, the profile can comprise a number of projections of sawtooth-like cross section so that pushing-on of the clips is facilitated but removal is impeded to a considerable extent.
The implant preferably consists of a metal which is well tolerated by the body, for example, of titanium or an implant steel. Provision can, however, also be made for the implant to consist of an absorbable material so that after a certain time the implant is decomposed and absorbed by the body.